Foliar Infection with Xanthomonas perforans Alters Response to Root-Knot Nematodes in Tomato

Plants experience multiple biotic stressors, both aboveground and belowground pathogens and pests. Although multiple pathogens infect plants naturally, research has been predominantly focused on binary interactions between the host and a single pathogen. Here, we investigated the outcome of single and simultaneous infection of tomato plants by parasitic root-knot nematode Meloidogyne spp. and foliar bacterial plant pathogen Xanthomonas perforans, which causes bacterial spot disease. We assessed the interactions of these pathogens and the disease outcome on nematode-resistant and susceptible varieties that are near-isogenic for the Mi resistance gene. Greenhouse experiments indicated that the presence of X. perforans supported the increased proliferation of root-knot nematode, specifically, incognita, on nematode-resistant cultivars containing the Mi resistance gene, with no significant influence on nematode-susceptible cultivars. On the other hand, Mi resistance gene-harboring tomato cultivars displayed increased susceptibility toward bacterial spot pathogen irrespective of the presence of nematode. These findings suggest that foliar bacterial infection may compromise Mi-mediated resistance to parasitic nematodes. It is essential to consider simultaneous infections by multiple pathogens when ensuring the long-term durability of the host resistance.